The present invention relates to a charged particle energy analyzer for such things as electron spectroscopy and ion spectroscopy, and, more particularly, to an energy analyzer of the type in which a low energy pass reflection filter and a high energy pass transmission filter are combined to measure the energy of charged particles generated from a sample.
FIG. 1 shows one of the conventional combinations of a low energy pass reflection filter and a high energy pass transmission filter provided for a conventional energy analyzer of a spherical mirror-spherical grid retarding potential type, as disclosed in U.S. Pat. No. 3,749,926 granted to Jerald D. Lee, issued on July 31, 1973, entitled "Charged Particle Energy Analysis".
The geometry of FIG. 1 contains a low energy pass reflection filter and a high energy pass transmission filter. The low energy pass reflection filter is featured by selectively reflecting charged particles having energy lower than a predetermined value. The high energy pass transmission filter is featured by selectively transmitting electrons having energy higher than a predetermined value.
In FIG. 1, the low energy pass filter is provided with a spherical mirror M having a curvature center O, and a spherical grid G.sub.1, which are arranged concentrically. The high energy pass transmission filter is provided with double spherical grids G.sub.2 and G.sub.3 having the curvature center O. The mirror M has a potential of V.sub.1. The grid G.sub.3 has another potential of V.sub.2. The grids G.sub.1 and G.sub.2 are placed in the same potential of V.sub.a and appropriate voltage are applied between the grid G.sub.1 and the spherical mirror M, and the grids G.sub.2 and G.sub.3.
When an injection point from which charged particles are diverged is disposed at a point S adjacent the center O, the charged particles having energy lower than e.vertline.V.sub.1 .vertline. are reflected by the mirror M, so that they are converged to a point adjacent the center O. They are diverged toward the high energy pass transmission filter. The charged particles having energy higher than e.vertline.V.sub.2 .vertline. are transmitted through the grid G.sub.3.
Finally, the charged particles having energy higher than e.vertline.V.sub.2 .vertline. and lower than e.vertline.V.sub.1 .vertline. can be collected by a detector disposed behind the grid G.sub.3. The charged particles diverged from the point S have energy of subtracting a potential applied to another grid from the energy of charged particles emitted from a sample, using a retarding field. By selecting the potential of this grid, the charged particles having a selected energy band width can be obtained.
However, since the low energy pass reflection filter and the high energy pass transmission filter must be disposed on opposite sides of the curvature center O, the energy analyzer must be large. Furthermore, a sample cannot be placed close to the point S because there is no space to set an exciting source such as an X-ray source or an electron gun, near the sample, so the apparatus therefore needs a complicated lens system to focus the charged particles from the excited sample surface to the point S.
Usually, the lens system reduces the transmission of the charged particles according to the particle energy.
Therefore, it is desired to provide a compact charged particle energy analyzer, which has no lens system.